In many applications it is desirable to have a variety of logic devices, memory devices, and devices capable of withstanding large transients (hereon referred to as power devices) all on a single substrate. One such type of power device is a double-diffused metal-oxide-semiconductor transistor (DMOS).
Heretofore most lateral double-diffused "metal" oxide semiconductor, LDMOS, structures built on a substrate with one or more other device structures were formed by first forming a high-voltage tank. After formation of the high-voltage tank, a second low-voltage tank (typically used as the backgate), of opposite conductivity type to that of the first tank, was formed within the first high-voltage tank, and active regions and gates were aligned to these tanks. The alignment of these to other existing structures is difficult.
Purely self-aligned LDMOS transistors cannot be easily integrated because a level of polysilicon is required early in the process. A purely photo-aligned device is difficult to control because the backgate leaves no marks for alignment, and channel length is alignment dependent.
It is, therefore, an object of the invention to form source/channel regions that are self-aligned and formed prior to the formation of the gate. It is a further object of the invention to perform a majority of the high-temperature process early in the process flow. Further objects and advantages of the invention will become apparent to those of ordinary skill in the art having reference to the following specification together with the drawings.